Cartel'. — Studies on the Chloroplasts of Desmids. /. 247 
any marked tendency to the parietal condition, and even in these one semi- 
cell in every case had distinctly axile chloroplasts. Sometimes in the same 
semi-cell one chloroplast was distinctly axile, whilst in the other half of the 
semi-cell there were signs of the tendency to the parietal condition. 
X. antilopaeum , X. cristatum , X. subhastiferum , var. Mrirrayip 
X . fascicidcitum :, and X. armatum . 
These remaining five species all have parietal chloroplasts, of which 
there are typically four in each semi-cell, two side by side on each front face 
(Figs. 106, 108, 113, 1 15, and 129). The parietal plates are usually very 
thin, and adhere closely to the cell-wall, corresponding fairly accurately with 
it in shape. In X. armatum the chloroplast plates are often prolonged at 
the angles of the cell to form projections which fill up the hollow bases of 
the branched spines (Figs. 129, 131, and 132). Very often there is an extra 
chloroplast on one or both front faces of the cell, either a small one, wedged 
in between the others, or one equal to them in size (Fig. 109). Rarely 
there is a fairly large number of small rounded plates, seven such chloro- 
plasts having been observed on one front face of a semi-cell of X. subhasti- 
ferum , var. Murrayi. Occasionally in X. armatum the chloroplast is in the 
form of a number of rather narrow parietal ribbons, running longitudinally, 
about six to eight in each semi-cell. 
The edges and external surface of the chloroplast plates in X. subhasti- 
ferurn , var. Murrayi , and X. cristatum , appear to be quite smooth and 
without projections of any kind ; cf. Figs. ]o8, 109, and 115. The same is 
usually the case in X. antilopaeum (Fig. 106), although it was occasionally 
noticed that in this species the surface of the chloroplasts was more irregular. 
In X . fasciculatum, however, the edges and surface of the plates were almost 
invariably covered with numerous short outgrowths (Fig. 113), and it was 
in this species that the maximum development of the chloroplast in this 
direction was noticed. In X. armatum the presence of such projections is 
a very variable character, being dependent on the amount of stroma-starch 
contained in the chloroplast. When little starch is present in the chloro- 
plast plates are very thin, their protoplasmic foundation is dense in 
texture, and in such cases a few slight prominent ridges (Fig. 130) or 
more numerous delicate projections usually stretch from their external 
surface towards the periphery. When more starch is present, the chloro- 
plasts become distended to three or more times their former thickness, and 
here the external surface is usually quite smooth, the delicate ridges having 
been quite obliterated in the process (Figs. 129 and 131). 
1 This Desmid was erroneously figured by W. and G. S. West (1904-11, vol. iv) as having an 
axile chloroplast with a single pyrenoid in each semi-cell. 
T 
